Chapter 13, Problem 60DSP

Interpretation Introduction

Interpretation:

The methylanilines, which can be formed by the reaction of $\text{p-bromotoluene}$

with sodium amide in ammonia, are to be determined.

Concept introduction:

Aryl halides, in the presence of a strong base, undergo substitution via elimination-addition mechanism.

In the first step, the base abstracts a proton attached to the ring carbon atom which is adjacent to the halogen. The proton and the halogen from adjacent carbon atoms are eliminated, and triple bond is created. This intermediate formed is benzyne.

The nucleophile then adds to any one of the triple bonded carbon atoms.

If the ring has a substituent other than halogen, the position of the nucleophile with respect to the substituent can be at two different sites, thus producing two different isomers.

In the overall reaction, the halogen is substituted by the nucleophile in product, and in the other product, the nucleophile gets attached to an adjacent carbon atom.